Could it be endometriosis?

I started having symptoms when I was 24 years old (I'm 28 now). It started as the usual menstrual pain though it would come 1-2 weeks before my period arrive.

The pain would spread from my abdominal area to the rectal area and sometimes to vaginal area. I'd feel worried about it but oftentimes, friends and family members would tell me it's just normal.

I first went to a doctor regarding the pain a year ago. She did an ultrasound on my pelvic area where she used an ultrasound device and scan the surface of my pelvis. She told me my uterus is healthy and I should not be worried.

She gave me Evening Primrose Oil which I took for 7 days, 1-2 weeks before my period. It didn't helped and the pain would not go away so I went to another doctor this year.

This doctor also did an ultrasound to me but this time, it's a trans-vaginal ultrasound, so he was able to detect cysts on my ovaries and fibroids on the lining of my uterus.

He prescribed birth control pills to me and it helped with the pain. During one of our meetings, I told him about endometriosis and he only told me "It could be that.." and asked me to continue the pills for 3 months and come back to him then for a follow-up check-up.

What should I do when the doctor could only tell me "It could be that.." like it was no big deal? It's as if he has no intention of further confirming if this is indeed endometriosis.

On the other hand, I was thinking he might wanna see the results after 3 months of me taking pills​ before he delved on to the possibility of endometriosis.

Also, the only symptoms I feel is the abdominal pain (that reaches to rectal area), could it be endometriosis?